Rustfmt is a tool for formatting Rust code according to style guidelines. By default, Rustfmt uses a style which conforms to the Rust style guide that has been formalized through the style RFC process. A complete list of all configuration options can be found in the Rustfmt GitHub Pages.
Formatting your Rust targets' source code requires no setup outside of loading rules_rust in your workspace. Simply run bazel run @rules_rust//:rustfmt to format source code.
In addition to this formatter, a simple check can be performed using the rustfmt_aspect aspect by running
bazel build --aspects=@rules_rust//rust:defs.bzl%rustfmt_aspect --output_groups=rustfmt_checks
Add the following to a .bazelrc file to enable this check during the build phase.
build --aspects=@rules_rust//rust:defs.bzl%rustfmt_aspect build --output_groups=+rustfmt_checks
It‘s recommended to only enable this aspect in your CI environment so formatting issues do not impact user’s ability to rapidly iterate on changes.
The rustfmt_aspect also uses a --@rules_rust//:rustfmt.toml setting which determines the configuration file used by the formatter (@rules_rust//tools/rustfmt) and the aspect (rustfmt_aspect). This flag can be added to your .bazelrc file to ensure a consistent config file is used whenever rustfmt is run:
build --@rules_rust//:rustfmt.toml=//:rustfmt.toml
Any target which uses Bazel generated sources will cause the @rules_rust//tools/rustfmt tool to fail with failed to resolve mod `MOD` . To avoid failures, skip_children = true is recommended to be set in the workspace's rustfmt.toml file which allows rustfmt to run on these targets without failing.
A test rule for performing rustfmt --check on a set of targets
ATTRIBUTES
| Name | Description | Type | Mandatory | Default |
|---|---|---|---|---|
| name | A unique name for this target. | Name | required | |
| targets | Rust targets to run rustfmt --check on. | List of labels | optional | [] |
A toolchain for rustfmt
ATTRIBUTES
| Name | Description | Type | Mandatory | Default |
|---|---|---|---|---|
| name | A unique name for this target. | Name | required | |
| rustc | The location of the rustc binary. Can be a direct source or a filegroup containing one item. | Label | optional | None |
| rustc_lib | The libraries used by rustc during compilation. | Label | optional | None |
| rustfmt | The location of the rustfmt binary. Can be a direct source or a filegroup containing one item. | Label | required |
This aspect is used to gather information about a crate for use in rustfmt and perform rustfmt checks
Output Groups:
rustfmt_checks: Executes rustfmt --check on the specified target.The build setting @rules_rust//:rustfmt.toml is used to control the Rustfmt configuration settings used at runtime.
This aspect is executed on any target which provides the CrateInfo provider. However users may tag a target with no-rustfmt or no-format to have it skipped. Additionally, generated source files are also ignored by this aspect.
ASPECT ATTRIBUTES
ATTRIBUTES
| Name | Description | Type | Mandatory | Default |
|---|---|---|---|---|
| name | A unique name for this target. | Name | required |